Morphology and Energetics of the Molecular Gas within a Core and a Diffuse Region in the Filamentary Dark Cloud GF 9

Abstract

We have performed a CO, 13CO, and CS survey of a dense core region (GF 9–Core) and a diffuse filamentary region (GF 9–Fila) within the dark cloud GF 9 (LDN 1082). Spectra in each line were obtained toward 120 positions within each region covering areas of 8' × 10'. GF 9–Core is associated with the Class 0 protostar IRAS PSC 20503+6006, while GF 9–Fila has no associated IRAS point sources. The median CO excitation temperature of the core region is 7.2 ± 0.5 K; for the filament region, the median temperature is 7.8 ± 0.5 K. The mass derived from the LTE isothermal analysis of 13CO is 53 ± 8 and 40 ± 6 M⊙ for GF 9–Core and GF 9–Fila, respectively. Using near-infrared extinction data to trace the H2 column density, the isothermal LTE assumptions for 13CO appear to break down at AV 3 mag. The near-infrared extinction data are used to correct the derived 13CO column densities, yielding mass estimates that are ~20% larger than the LTE-derived masses. The average H2 volume densities for GF 9–Core and GF 9–Fila are ~5000 ± 700 and ~1700 ± 200 cm-3. Each region contains a 15 ± 3 M⊙ centrally condensed CS core, which is approximately 3 times more dense than the ambient 13CO regions. In GF 9–Core, the high-density gas core appears to be physically associated with the IRAS point source. Both high-density cores appear to be in virial equilibrium; however, the CS line widths in GF 9–Core are almost twice as large as those measured in GF 9–Fila. Because GF 9–Core is associated with the Class 0 protostar PSC 20503+6006, the CS line widths may be enhanced by outflow or infall motion. The additional nonturbulent line-broadening component caused by outflow/infall motion required to explain the line width implies a supersonic velocity of at least 0.3 km s-1 (Mach 1.5).